Welding cast iron

Brazing is often preferred with unknown materials as cracking after welding is very common.

The pipe is cast iron.

Yes. Cast iron is a bitch to weld without cracking later. Ideally it needs to be brought up to close to melting temperature, welded and then cooled very slowly. Having said that when a threaded boss on an old Marina engine of mine needed repairing 30 years ago my uncle just filled it with weld with an old stick welder with some randomly selected welding rod, drilled and tapped it and it was fine. However it was a solid lump well attached to a solid engine block. Anything fragile like your pipe is a different kettle of piscean vertebrates.

Cast is VERY difficult to weld properly. the usual way is to slowly heat the piece up to red hot, weld it with appropriate rods and cool it down slowly. Unless you know someone with the right skills its going to be expensive. I'd be inclined to try brazing then make a shaped clamp plate to go over the flange and once complete hide it with paint. Is it an exhaust pipe from some static engine or something else?

The pipe is bolted inside a firebox that's red hot and contains steam at 110 psi.

I would be extremely pessimistic of any result. Cast iron can be welded in the manner described by other posters, but I would expect re-cracking of the flange through the force exerted by the bolts when assembled.

I would be more tempted to make a mild steel flange of the same size, cut the old one off and braze or weld the end of the pipe onto the new flange.

Are you sure it's cast iron? Is the material too hard to file?

Bronze welding may be more suitable as much less heat going into the pipe, you can also build up thickness and shape easily.

Sorry, I meant unknown type of cast iron. It has several forms some of which are unweldable because the welding changes the characteristic of the cast iron making it very brittle and cracking inevitable. .

Have you thought of recasting the whole thing?

Is replacing the entire pipe* an option? My (limited) understanding of welding cast iron is that quite often it can break again in the future, particularly in high stress environments, and it looks like that pipe as a whole has had a hard life (understandable, given where it came from).

• either with something manufactured to be identical to the original, or

- in a restoration context - with something that performs the same function, where you'll keep the damaged original in storage as part of the project.

cheers

Jules

In that case I would be inclined to change to a fabricated stainless steel version. The stainless will resist the flue gases and have a better long term bursting strength. Patched up cast iron with 110psi steam inside it isn't something I would want to get too close to.

That's probably not permissible, for most steam boiler certification (depends where in the world you are).

The problem is that an old boiler doesn't meet modern design standards

- often because there's no discernible "design" recorded for it. If it exists, hasn't killed anyone lately, and some basic objective tests say that it's in good condition for its original design, then the design can be grandfathered in and the boiler can be ticketed.

OTOH, if you _change_ its design, even in a fairly minor way, then you have a new design to contend with, and you're into a world of paperwork. It also (and this is the problem) loses grandfathering status for other parts of the boiler. You may very well make an improvement to one dubious part of the boiler, only to then fail all hope of certification because some other non-problematic aspect is now seen as inadequate.

This catch 22 is a reason for scrapping many contemporary boilers that in a more holistic world could continue operation. You may find an inspector with literally half a clue, who won't pass the old part because it's knackered, but won't allow it to be replaced appropriately without condemining the rest of the boiler.

OTOH, don't introduce stainless into an old boiler unless you know what you're doing and you also keep a close eye on alloys. You can really screw things up with galvanic corrosion, if you're not careful.

On the whole, I'd take the whole flange off, and weld on a whole new flange. This gives you much better options for cleaning up before the weld.

Cast iron welding is no big deal (manual arc, nickel rod). It's no harder than brazing and generally gives a better result. The trick for both is to pre-heat well with a gas torch beforehand, cool slowly afterwards (bucket of wood ash) and (for welding with a nickel rod) peen the weld after it's welded and while it's still hot.

Price of nickel rods is a bitch. If you can buy a handful, then fine. Otherwise a boxful is spendy for a one-off job, so it's usually easier to go to someone who already owns a box (and probably welds CI all day, as many welders in the repair trade do).

I'm rather puzzled to see a CI pipe with a CI flange used like this on the inside of a firebox though. I'm actually surprised it has passed any inspection for the last hundred years.

I fully agree. You should get some mechanic from a museum or something who has

You'd be much better off scrapping the boiler and replacing it with something entirely new. And instead of a firebox, maybe an electric heater? These are much safer. Or a modern condensing boiler, which is also more efficient! Yes!

Thomas Prufer

• There are actually few around, as East Germany ran steam locomotives in regular service until recently, relatively speaking.

Actually the pipe is at the other end of the boiler from the firebox, so not red hot. But still hot! The welding will be done by the best experts around, and inspected by a boiler inspector, as usual.

You must be new here. Matty IS someone working in a museum, who repairs ancient things, and the boiler he's talking about is undoubtedly a restoration job. I suspect that replacing the boiler with a modern version would defeat the whole purpose of the enterprise. Nevertheless your point about the advisability of attempting a repair may well be correct.

I now have this mental picture of a steam train, sans boiler, and modern combi bolted to the front! Still saves shovelling coal, but might need a long gas hose.

Efficiency is unimportant. We have thousands of years worth of coal here. Shoveling coal keeps the driver fit. And he can cook his lunch along the way: